Telecommunication is the transmission of signals over a distance for the purpose
of communication.
Telecommunications is a general term for a vast array of technologies that send
information over distances. Mobile phones, land lines, satellite phones and voice
over Internet protocol (VoIP) are all telephony technologies -- just one field of
telecommunications. Radio, television and networks are a few more examples of
telecommunication.
While most people associate telecommunications with modern technologies, the
strict definition of the term encompasses primitive and even ancient forms of
telecommunication. Among these is the use of smoke signals as a kind of visual
telegraph. Puffs of smoke were time-released by smothering a fire with a blanket,
then quickly removing and replacing the blanket. Widely used by the American
Indians, smoke signals could communicate short messages over long distances,
provided a clear line of sight.
Other forms of early telecommunications include relay fires or beacons. Used
foremostly in warfare, relay fires required a handful of men posted along a range
of hilltops, with the last man closest to the area where troop movement was
expected. When armies were spotted in the distance, he would light a bonfire.
The fire could be seen from a good distance away by the next man in the relay,
who would in turn light his own bonfire, and so the fires were lit in succession
along the range, creating an effective telecommunications signal that traveled
back over several miles in a relatively short period of time. Finally, the last man in
the relay would light a beacon to signal his army below that the opponent was
en-route.
The arrangement of a ship's flags and semaphores were other forms of
telecommunications. A semaphore was a mechanical device atop a tower with
paddle-like blades or flags. The device would be set in a specific position to
communicate information.
Throughout the 19th century, telecommunications devices became more
sophisticated with the advent of electricity, leading to the telegraph, Morse code,
and signal lamps. A signal lamp, the optical version of the telegraph, is a
powerful lamp with shutters that block the light in long or short durations to
translate to the dots and dashes of Morse code. A heliograph is another optical
telegraph -- a mirror used to reflect light to mimic a signal lamp.
In the 20th century, telecommunications reached beyond our planet. In June
1969, the world watched and listened as astronauts walked on the moon. Twenty
years later, in August 1989, we would see pictures of Neptune arrive back from
the Voyager 2 spacecraft, riding radio waves that traveled over roughly three
billion miles (4.8 billion km) to reach us in a matter of a few hours.
Strides in telecommunications have changed the world immeasurably. While
pockets of humankind were once isolated from each other, people now have
multiple ways to see and hear what is occurring on the other side of the world in
real time. Satellite technology, television, the Internet and telephony keep the
globe connected in a humming buzz of interactive voices and pictures. In short,
telecommunications has come a long way from smoke signals.
1.2.2 Duplex Connection 
